The present invention relates generally to improved nonaxisymmetric high aspect ratio afterburner convergent nozzles for use with aircraft jet propulsion engines; and, more particularly, to a nonaxisymmetric high aspect ratio afterburner convergent nozzle of the type employing a static pressure balance chamber and which finds particularly advantageous use in military-type aircraft requiring low observable infrared and cross-sectional radar detection. In its principal aspects, the invention is concerned with a jet propulsion engine afterburner nozzle which can be mounted on an engine suspended from the airfoil's wing spar structure and where the nozzle can be readily shifted between a convergent dry (cruise) attitude and a wet (afterburn) attitude; yet, wherein the trailing edge line-of-sight is maintained at a minimum included angle .theta.--preferably on the order of from about 5.degree. to about 10.degree.--with respect to the wing chord reference plane when the nozzle is in its dry or cruise position.
In the design of military jet aircraft, one of the prime considerations is to locate the jet engine relative to the supporting airfoil structure in such a manner that enemy aircraft systems are precluded from looking into the engine's relatively large nozzle opening and detecting hot engine parts. It has, of course, long been recognized that one "solution" to this problem is to mount the jet engine tightly beneath the airfoil so as to provide a low profile and a minimal trailing edge line-of-sight into the nozzle. Unfortunately, however, such jet engine nozzles must be controlled so as to vary the nozzle opening between cruise and afterburn positions--i.e., between dry and wet nozzle positions. Consequently, prior art approaches to this problem have generally required relatively complex structures including static pressure load balance chambers disposed above the exhaust nozzle and within the critical internal wing spar structural envelope. The additional structural components, seals, maintenance and envelope space required have, in turn, increased the weight of the engine nozzle and the loading of the rear engine support frame. A typical example of such a device is that disclosed in McCardle, Jr. et al U.S. Pat. No. 4,000,611. However, despite such efforts at the expense of critical wing spar structural space, the trailing edge line-of-sight has remained at unacceptably high angles (on the order of from about 35.degree. to on the order of 40.degree.) with respect to the wing chord reference plane.
Another common prior art approach has been the use of augmented deflector-type exhaust nozzles which may have additional application for short take-off and landing (STOL) and vertical take-off and landing (VTOL) type aircraft such, for example, as those disclosed in: Nash U.S. Pat. No. 3,979,067; Nash et al U.S. Pat. Nos. 4,000,610 and 4,073,441; and, Wakeman et al U.S. Pat. No. 4,000,612. However, the complex linkages and deflector-type vanes employed have not led to minimizing the trailing edge line-of-sight.
Other prior art patents which are of general interest for their disclosures of tiltable nozzles or the like employing a central trunnion-type mounting include: Jewell U.S. Pat. No. 3,003,312; Gaubatz U.S. Pat. No. 3,032,982; Fisher U.S. Pat. No. 3,210,936; Zirin U.S. Pat. No. 3,319,892; and, Connolly U.S. Pat. No. 3,362,646. Such patents do not, however, relate to the problem of minimizing the trailing edge line-of-sight into the nozzle openings, nor do they pertain specifically to nonaxisymmetric high aspect ratio afterburner convergent nozzles of the type employing static pressure balance chambers.